Energy-absorbing materials (EAMs) that reduce the amount of reflected electromagnetic energy from their surface have many applications, such as in the stealth technology used to disguise a vehicle or structure from radar detection to foam absorbers in anechoic chambers, solar light energy harvesting in thermal photovoltaics, to infrared sources and detectors. The resulting interest in such systems had lead to the development of many methods and manufacturing techniques to improve the performance of radiation absorbers, such as impedance-matched surfaces in microwave and radar electronics, anti-reflection coatings in optics, and resonance-based metamaterials.
However, despite significant progress in this field over the years, existing methods to reduce reflected radiation are often substantially degraded by damage to the surface due to, for example, exposure to the environment. The resultant surface defects, including moisture adherence, may lead to a significant amount of back-scattered or reflected radiation, with the resulting possibility of detection for a stealth aircraft, performance deterioration for solar collectors or other such performance shortfalls.
In recent years, there have been discoveries in which the response of engineered materials to electromagnetic waves behaves in unanticipated ways. These materials have generally described as metamaterials; however, earlier examples of such materials were termed “artificial dielectrics.” Since the field now encompasses engineered aspects of permeability as well as the permittivity, the general term metamaterials has become more conventional to use. A metamaterial may be engineered so as to be strongly anisotropic in one or more of permeability and permittivity and to exhibit well controlled properties that are not available in existing natural materials.